A Liquid Crystal Display (LCD) device may include an array of Liquid Crystal (LC) elements, which may be driven, for example, by Thin Film Transistor (TFT) elements. Each full-color pixel of a displayed image may be reproduced by three sub-pixels, each sub-pixel corresponding to a different primary color, e.g., each full pixel may be reproduced by driving a respective set of LC elements in the LC array, wherein each LC element is associated with a color sub-pixel filter element. For example, three-color pixels may be reproduced by red (R), green (G) and blue (B) sub-pixel filter elements. Thus, each sub-pixel may have a corresponding LC element in the LC array. The light transmission through each LC element may be controlled by controlling the orientation of molecules in the LC element. The response time of the LC element may be related to the length of time required for changing the orientation of the LC molecules. This may introduce an inherent delay in the process of modulating the transmittance of the LC elements.
The LCD device may be implemented to display scene images, which may include, for example, a sequence of frames, in accordance with a video input signal. Unfortunately, due to the inherent delay in mobilizing the molecules in the LC elements, the displayed image may appear blurred to a user, e.g., if the response time of the LC elements is significant in relation to the frequency at which the frames are displayed. In other words, the response time of the LC elements may depend on the value of the activation voltage of both a previous frame and a current frame. A response time that is longer than a refresh cycle of a pixel or sub-pixel corresponding to the LC element may result in the blurring effect, particularly in images or image portions with abrupt changes, e.g., images of fast moving objects. It may also result in a color shift effect of displayed colors. FIG. 1(A) illustrates a pixel response to an input pulse signal.
In order to reduce such “blurriness” of displayed images, the LCD device may implement a Response Time Compensation (RTC) method, for example, a Feed Forward Driving (FFD) method, to compensate for the slow pixel response. The FFD method may include a FFD module able to control a LC element based on a comparison between sub-pixel values of the LC element in a previous frame and in a current frame. For example, a Look Up Table (LUT) may be used to provide the LC element with a control signal based on the previous sub-pixel value and the current sub-pixel value.
FIG. 1(B) illustrates a conventional driver circuit for pixel response compensation. In order to create an overdrive signal to the pixel, a previous frame is stored in a frame buffer 101. Voltage values of pixels from a current frame and a previous frame may then be fed into a computation circuit 102, which may include a central processing unit (CPU), a look-up table (LUT), or a combination of both. The computation circuit 102 may subsequently output a compensated voltage to be applied to a column driver 103 to drive the pixel. Such conventional compensation method requires the use of frame buffer 101 having a sufficient memory capacity in order to store sub-pixel voltage values for the entire previous frame. The required size of such memory may be relatively large, e.g., a memory of approximately 6 Megabytes (MB) may be required for storing the sub-pixel values of a three-primary, e.g., RGB, display device having a 1080 by 1920 pixel resolution. The required size of the memory may be reduced, e.g., down to about 600 Kilobytes (KB), using suitable compression techniques, which may result in loss of detail and/or quality at varying degrees, as is known in the art.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components included in one element. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. It will be appreciated that these figures present examples of embodiments of the present invention and are not intended to limit the scope of the invention.